Interested in Missing Tennessee Student?

There have been no credible sightings of 50-year-old Tad Cummins and 15-year-old Elizabeth Thomas in the two weeks they've been missing, officials said. Her sister, Sarah Thomas, told ABC News that he showed up at her sister's workplace multiple times, including the Saturday before they disappeared.

Thomas would ask co-workers to tell Cummins that she wasn't there, Sarah Thomas said, "and she would go and hide until he left."

According to Sarah Thomas, her sister hid in the bathroom at work multiple times. Sometimes she couldn't hide because she was at the cash register, Sarah Thomas said.

Pictured is Elizabeth Thomas, the subject of a statewide AMBER Alert in Tennessee.

As the manhunt for the two intensifies, "it feels like she just vanished," Sarah Thomas said.

Cummins is wanted on allegations of aggravated kidnapping and sexual contact with a minor. An Amber Alert has been issued for Thomas.

Her father, Anthony Thomas, said, "We just live for that day when we're going to get a phone call that says, 'I'm all right. I need somebody to come and get me.'"

Thomas family attorney Jason Whatley told ABC News last week that Cummins "is a 50-year-old authority-figure predator. That's what he is. He has preyed on her."

"She is under his spell, and she is being controlled by him, and that is what is so scary," Whatley said.

The Tennessee Bureau of Investigation

Pictured is Tad Cummins, who is on the Tennessee Bureau of Investigation's 'Top 10 Most Wanted' list.

The Tennessee Bureau of Investigation said that Cummins, who was fired one day after the alleged kidnapping, "may have been abusing his role as a teacher to groom [Elizabeth] ... in an effort to lure and potentially sexually exploit her."

Investigators have uncovered email draft messages between Thomas and Cummins, which authorities said show a romantic relationship between the two. According to authorities, after one of them would write a message, he or she would save the message as a draft, and the other person would log on, read the message and delete it.

Cummins, a married father and grandfather, researched teen marriage online, specifically the age of consent, according to law enforcement officials.

One of Thomas' schoolmates reported seeing her and Cummins kiss in his classroom on Jan. 23, according to a school district investigative report, but both denied the claim. A school report from January reads that neither one "admitted to behaving inappropriately towards the other."

Tennessee Bureau of Investigation

The Tennessee Bureau of Investigation released a photo of Tad Cummins and Elizabeth Thomas at school in January.

Sarah Thomas told ABC News her sister was bullied in school by students and teachers after the reported kiss.

TBI spokesman Josh DeVine told ABC News last week that the duo could be "off the grid" in a rural area at this point.

Cummins is believed to have watched a TV show about living off the grid before the pair disappeared, law enforcement sources told ABC News. Three days before the alleged kidnapping, he did online research about his car "to determine if certain features could be tracked by law enforcement," the TBI said. He also researched if his SUV was suitable for camping, according to law enforcement officials.

He is described as 6 feet tall and about 200 pounds. He may be driving a 2015 silver Nissan Rogue with Tennessee license plate number 976-ZPT.

Thomas is described as about 5 feet tall. She was last seen wearing leggings and a flannel shirt.

Authorities are asking that anyone with information call 1-800-TBI-FIND and that anyone who sees a car with Tennessee license plate number 976-ZPT call 911. A $1,000 reward is available for information leading to Cummins' arrest.